The small number of species found in Australian inland waters is partly because Australia is the driest continent on earth. Rainfall is sporadic over much of the continent, and fishes cannot live in many of the desert regions of South Australia and Western Australia. Most freshwater species are found in tropical or subtropical regions.[1]

A large proportion of freshwater species are endemic to Australia. Australia is unique in that the Percicthyidae (Temperate Perches) family and other families suspected in reality to lie within it (e.g. Gadopsidae, Nannopercidae) have risen to prominence in and dominate many of its freshwater systems, in contrast to the Northern Hemisphere where freshwater fish faunas are overwhelmingly dominated by the Cyprinidae (Carp) family. (No Cyprinid species is native to Australia). Due to the illegal introduction of Carp (Cyprinus carpio) the Cyprinidae family is now present in a destructive form in Australia. The Galaxiidae have also risen to unusual prominence in Australia, with the bulk of the world's Galaxias species found in Australia and its neighbouring land mass New Zealand.

The most important freshwater system in Australia is the Murray-Darling Basin which drains approximately 13% of the continent and contains some of Australia's most significant freshwater fish species including the Murray Cod, Australia's largest freshwater fish.

Australian freshwater fish have not fared well since European settlement of Australia in 1788. The majority of Australian freshwater fishes are poorly understood and are under threat due to human activities such clearing of riparian vegetation and siltation associated with agricultural practices, snag removal, overfishing, river regulation through dams and weirs, introduced fish and diseases. Two native fish populations that may have been separate species or sub-species, the Richmond River Cod and the Brisbane River Cod, are extinct, and a number of other species are listed as endangered or critically endangered.